The RA53B is a high powered headphone amplifier with five 1/4" And 1/8" (3. 5mm) headphone and earphone outs. Two RA53B units may be linked together and mounted side-by-side in a universal rack tray for a total of 10 outputs. # 5: 1/4" Trs headphone outputs with level control. Lots of gain. 1/4" And RCA right and left inputs. Inserts on two channels. 1/4" Trs stereo input, 1/4" Mono input. Link input/output for connecting two units together. Input impedance: 10 K ohms Maximum Input level: +18 dbvmax gain: 26 dB per channel output power: 221 mW per side, 442 mW per channel (@ 32 ohms)output impedance: 10 ohms/N ratio: >90 dbthd: